Monorail conveyors are used to convey articles such as vehicles or other articles which are difficult to move from station to station. Monorail conveyors continuously move articles and do not permit articles to be stopped to perform assembly steps. As a result, assembly steps must be brief or the assembly station must allow for movement of tools or workers with the moving article.
"Power and free conveyors" have been developed in which a double track is provided for the entire length of the conveyor system with one track being used for conveying articles between stations and a second track being used to provide movement separate from the primary conveyor. The primary disadvantage of power and free conveyors is the cost of such systems. The high cost of such systems is necessitated by the complex structure of the carriers and the high cost of providing a complete double track system which extends the full length of the conveyor system. One example of a power and free conveyor is disclosed in U.S. Pat. No. 4,287,829 to Wakabayashi, which discloses a carrier stopping device adapted to either engage a trolley so that the trolley is driven by a conveyor chain or to disengage the trolley from the conveyor chain so that the trolley is permitted to move freely along the guide rail.
Another example of a conveyor system, which includes a detachable carrier is disclosed in U.S. Pat. No. 2,816,643 to Klamp. In this patent workpieces are advanced by a main conveyor and a secondary conveyor. The carriers moved by the conveyors include complex movable hooks which are lowered by cam mechanisms to engage shafts which move the carriers along the conveyors. The complex nature of the carriers disclosed in the Klamp patent makes the carriers expensive and subject to malfunction.
In general, the prior art has failed to provide a simple and effective conveyor system, which in a cost-effective manner provides a mechanism for transporting heavy articles, such as automotive bodies, between workstations where the article can be operated on and moved independently of the primary monorail system.